The invention relates to a method of manufacturing cellulose fibres with reduced orientation and a reduced modulus, and to fibres produced according to this method.
Due to high investment costs, and in particular due to the high degree of stress on the environment, there is a considerable interest in finding alternatives to the viscose process, according to which at present the majority of cellulose regenerate fibres are manufactured. Among the most promising methods is the spinning of solutions of cellulose in amine oxides, preferably in N-methyl-morpholine-N-oxide (NMMNO), not least because in this way the complex path via derivatising of the cellulose is avoided. It is known from DE 28 30 685 and 20 DD 142 898 as well as from EP 0 490 870, that cellulose is soluble in a NMMNO water system, and can be processed to produce textile fibres by spinning in a mostly aqueous NMMNO solution.
Although the NMMNO process is already used on a large industrial scale, and the fibres produced thereby have proved successful for some textile applications, the latter reveal a series of differences in comparison to the fibres produced by the viscose process, and therefore are not usable in the conventional way in the textile field; among other things they reveal brittleness and a tendency to fibrillation in the wet condition. In addition, the values achieved for tensile stretch are unsatisfactory. A disadvantage is also seen in the fact that the range of variation of the physical textile characteristics is restricted when the manufacturing conditions are altered.
For the fibres produced according to the NMMNO process, in comparison to viscose fibres, high strengths and moduli are characteristic. Thus the tear strengths generally lie in a approximate range of about 20 to 50 cN/tex, and the initial moduli in a range of over 1500 cN/tex. This means that the strengths are highly satisfactory, and are often higher than necessary. On the other hand, however, the high modulus as a rule is caused by a high orientation of the fibres, and the high orientation is decisively responsible for a high tendency of the fibres to fibrillation. This high tendency to fibrillation however has an unfavourable effect for many applications of the fibres in the textile field.
One possibility of reducing the modulus to a limited degree and thus to reduce the tendency of the fibres to fibrillation, resides, instead of the normally-used spinning bath of an aqueous NMMNO solution, in using a solution of NMMNO in isopropanol or amylalcohol (SU 1 224 362) or to add specific hydrophilic additives (DE 95 104 358) both to the spinning solution and to the spinning bath. The slight reduction in strength resulting can be tolerated, as the fibres still have strengths corresponding to those of viscose fibres. In all, these methods however still leave something to be desired as regards the brittleness of the fibre and as regards the possibility of controlling the physical textile characteristics of the fibres by changing the manufacturing conditions.
Thus it remains a central problem to produce flexible cellulose fibres with a low tendency to fibrillation from NMMNO solutions, and to influence the spinning process in such a way that fibres can be produced thereby which cover the entire range of application of textile viscose fibres.
Proceeding from this point, it is the object of the present invention to provide a method for manufacturing flexible cellulose fibres with reduced brittleness and tendency to fibrillation.